1. Field of the Invention
This invention relates to a data reproducing apparatus and also to a data reproducing method. More particularly, it relates to a data reproducing apparatus to be suitably used for an AV server in a broadcasting station.
2. Description of the Prior Art
The increased number of channels that have become available for accessing to various types of information due to, if partly, the development of CATV (cable television) in recent years has by turn given rise to a strong demand for novel audio/video data recording/reproducing apparatus adapted to recording and reproducing different sets of audio/video data concurrently with a single apparatus. As a matter of fact, apparatus referred to as a video server (or an AV (audio and/or video) server) and adapted to concurrently recording different sets of audio/video data in and also reproducing such data from randomly accessible recording means such as hard disks have getting popularity to meet this demand.
Generally, a video server installed in a broadcasting station is required to show a high data transfer rate and have a huge recording capacity in order to meet various requirements including a high image and sound quality and a long recording time. Thus, attempts have been made to produce a high data transfer rate and a high recording capacity by introducing a data recording/reproducing apparatus capable of dealing with a plurality of hard disks (hereinafter referred to as HD) units concurrently and storing parity data in the apparatus in advance so that the overall reliability of the apparatus may be maintained if one or more than one of the HD units fail. With such an arrangement, it is possible to realize a multi-channel video server adapted to a variety of applications such as VOD (video on demand) and NVOD (near video on demand) systems, where same source data comprising a plurality of different sets of audio/video data are recorded in a distributed fashion and then reproduced simultaneously or with slight time differences before they are transmitted through a multiple of channels.
The data recording/reproducing apparatus used in such a video server is based on the RAID (redundant arrays of inexpensive disks) technology of utilizing a plurality of hard disk drives (hereinafter referred to as HDDs), each being adapted to drive a plurality of hard disks, as described in Patterson et al. (xe2x80x9cA Case for Redundant Arrays of Inexpensive Disks (RAID)xe2x80x9d, ACM SIGMOND Conference, Chicago, Ill., Jun. 1-3, 1998.)
According to the above paper, the RAID technology may be classified into five categories, RAID-1 through RAID-5. Category RAID-1 used to write same data in a pair of HDDs. With Category RAID-3, the input data are divided into groups of data having a predetermined length and recorded in a plurality of HDDs, while a parity data is generated as exclusive OR of the corresponding data blocks of each HDD and written in another HDD. With Category RAID-5, on the other hand, data are divided into large units (blocks) and the data of each unit are recorded in an HDD as data block, while the outcome of exclusive OR (a parity data) of the corresponding data blocks of each HDD is recorded in other HDDs as a parity block in a distributed fashion.
For the remaining aspects of RAID, reference should be made to the above identified paper.
An AV server as described above comprises a data storage consisting of a plurality of hard disks for storing AV data, a plurality of AV data input/output interfaces (hereinafter referred to as ports) for inputting AV data into and outputting such data from the data storage and a system controller for controlling the operation of the entire system. Each port has a memory for regulating the timing of retrieving out AV data from and that of storing AV into the data storage. Then, an AV server having the above described configuration performs processing operations concurrently for a multiple of channels as the system controller controls the ports in such a way that they are used evenly and cyclically on a time division basis with a predetermined period. More specifically, each port processes AV data for a single channel on a time division basis so that, as a result, AV date are processed for all the channels simultaneously by the ports, the number of which is equal to that of the channels. Therefore, with such an AV server, time slots are allocated to the ports of the multiple of channels periodically in a rigid fashion. Then, as a general practice, the length of each time slot is made as short as possible in order to minimize the queuing time of each port, provided that the time length required for each port to read and reproduce a given volume of data from the memory at an ordinary rate is secured.
An AV server used by professionals in broadcasting stations and other similar facilities are required by necessity to show a quick responsiveness particularly in the initial stages of the AV data reproducing operation. Additionally, since AV data will have to be reproduced with variable speed for frequent high speed or reversal replaying in AV data editing sessions, a quick responsiveness and an enhanced operability are essential particularly when the replay speed has to be accelerated for a shift from normal speed to high speed or vice versa and when the current forward replaying has to be switched to backward replaying or vice versa. More specifically, when an command is given for a replay speed change, such a change has to take place very smoothly in producing the specified speed and/or running direction without giving rise to the effect of a slow-speed film.
However, with the known AV server, the length of each time slot is defined by referring to the normal replay speed and hence they are accompanied by the following problems when they are used for variable speed.
For example, in a known AV server provided 10 ports and hence adapted to perform input/output operations through 10 channels, a second is divided into 10 time slots, which are then evenly allocated to the 10 channels so that AV data for a second (30 frames) are read out in a time slot. However, the operation of reading out data at such a rate is insured only when the hard disk from which it is reading out data has a continuous recording area or several distributed areas at most for a second of operation so that the operation can proceed effectively at least for a second for reading out the specified contents.
Thus, with such a known AV server, storage areas on the currently active hard disk have to be accessed discontinuously in a high speed AV data reproduction mode of operation so that a large portion of the time dedicated to the data reproducing operation is actually consumed for the accessing process at the cost of the time necessary for reading data. More specifically, when reading AV data from the hard disk for frames selected for high speed replaying as a function of the required magnification ratio of replay speed, distributed areas have to be accessed on a frame by frame basis so that consequently AV data for only two or three frames can be read out in a single time slot in the worst case where the time is mostly consumed for seek operations.
Therefore, the above described time slot allocation scheme is not very effective and the volume of AV data that can be read out in a single time slot is reduced from the intended volume of data good for 30 frames to the volume of data good for only two or three frames. The net result is that the number of data sheets reproduced per unit time is reduced significantly particularly during high speed data reproducing operations so that images may be displayed like those of a slow-speed film and the operation of searching out any wanted image can become very cumbersome in the editing session.
Secondly, such a known AV server cannot respond to a command for an operation of accelerating from normal replaying to high speed replaying, decelerating from high speed replaying to normal replaying or reversing the reproducing direction issued by way of the control panel until the next time slot allocated to the related channel comes to make the system rather clumsy and inefficient.
In view of the above identified problems and other problems, it is therefore the object of the present invention to provide a data reproducing apparatus and a data reproducing method that can reproduce images in a variable speed replay mode by quickly realizing the specified speed and/or direction of replaying operation, be it high speed replaying, acceleration, deceleration or reversing, without giving rise to the effect of slow-speed film.
According to the first aspect of the invention, there is provided a data reproducing apparatus characterized by comprising:
a data accumulation means consisting of a non-linearly accessible recording medium for accumulating data including video data;
a plurality of data reproducing means adapted to storing the data read out from said data accumulation means in respective memories, converting said data stored in the memories to a predetermined data format and outputting the data; and
a control means for allocating time slots to said data reproducing means with a predetermined cycle period and controlling said data reproducing means so as to cause them to read out said data from said data accumulation means and store them in said respective memories in said respective time slots;
each of said memories including at least three banks, each having a capacity for storing data for the time slots of each said predetermined cycle period;
said control means assigning to the data reproducing means operating for variable speed replaying the time slots to be allocated to the remaining data reproducing means.
According to the second aspect of the invention, there is provided a data reproducing method for a plurality of data reproducing means to read data from a non-linearly accessible recording medium, store them in respective memories of said data reproducing means and convert them to a predetermined format before outputting them in the respective allocated time slots, comprising:
a first step of assigning to the data reproducing means operating for variable speed replaying the time slots to be allocated to the remaining data reproducing means; and
a second step of causing said data reproducing means to read out data corresponding to the time period of said assigned plurality of time slots from said recording medium in the assigned time slots of said predetermined cycle period and store them in said memory.
According to the third aspect of the invention, there is provided a data reproducing apparatus characterized by comprising:
a data accumulation means consisting of a non-linearly accessible recording medium for accumulating data including video data;
a plurality of data reproducing means adapted to read data from said data accumulation means, store said data into one of at least three banks constituting each of the memories belonging respectively to said data reproducing means and output the stored data in allocated time slots; and
a control means for allocating time slots to said data reproducing means;
upon receiving a control command for double speed replaying, the data reproducing means with the received control command reading out data corresponding to the time period of said allocated time slots of a predetermined cycle period from said data accumulation means in the closest one of the time slots allocated by said control means, thinning out said data so as to be output continuously during the time period down to the third time slot allocated by said control means to the data reproducing means with the received control command, if said first time slot not being the time slot allocated to any of the remaining data reproducing means in the time slot cycle period of receiving said control command, and outputting said thinned out data from said first bank;
said control means assigning said second time slot to be allocated to any of the remaining data reproducing means during said time period from said first time slot to said third time slot to said data reproducing means with the received control command.
According to the fourth aspect of the invention, there is provided a data reproducing method for a plurality of data reproducing means to read out data from a non-linearly accessible recording medium in the respective time slots allocated to them, storing them into one of at least three banks constituting each of the memories belonging respectively to said data reproducing means and outputting the stored data, comprising:
a first step of reading out data corresponding to the time period of said allocated time slots of a predetermined cycle period in the closest first one of the time slots allocated to the data reproducing means receiving a control command for double speed replaying and storing the data in the first bank of the memory of said data reproducing means;
a second step of thinning out said data so as to be output continuously during the time period down to the third time slot allocated by said control means, if said first time slot not being the time slot allocated to any of the remaining data reproducing means in the time slot cycle period of receiving said control command, and outputting said thinned out data from said bank;
a third step of assigning the second step to be allocated to any of the remaining data reproducing means during said time period from said first time slot to said third time slot to said data reproducing means with the received control command; and
a fourth step of storing said data corresponding to the time period of said time slots of a predetermined cycle period into the second bank of said memory and outputting said data for said double speed replaying in the time slot assigned in said third step.
According to the fifth aspect of the invention, there is provided a data reproducing apparatus characterized by comprising:
a data accumulation means consisting of a non-linearly accessible recording medium for accumulating data including video data;
a plurality of data reproducing means adapted to read data from said data accumulation means, store said data into one of at least three banks constituting each of the memories belonging respectively to said data reproducing means and output the stored data in allocated time slots; and
a control means for allocating time slots to said data reproducing means;
upon receiving a control command for reversing the replaying direction, the data reproducing means with the received control command outputting the data stored in the first bank of said memory in the reverse direction during the time period down to second time slot allocated to said data reproducing means and destructing the data stored in the second and third banks of said memory, thereby reading out data corresponding to the time period of the time slots of a predetermined cycle period continuously from said recording medium in the closest first time slot assigned to said data reproducing means with the received control command from the time of receiving said control command in the direction reverse to that of said data output from said first bank and storing said data into the second bank.
According to the sixth aspect of the invention, there is provided a data reproducing method for a plurality of data reproducing means to read data from a non-linearly accessible recording medium, store them in respective memories of said data reproducing means and convert them to a predetermined format before outputting them in the respective allocated time slots, characterized by comprising;
a first step of, upon receiving a control command for reversing the replaying direction, outputting the data stored in the first bank of the memory of the data reproducing means with the received control command in the reverse direction during the time period down to second time slot allocated to said data reproducing means;
a second step of destructing the data stored in the second and third banks of said memory;
a third step of reading out data corresponding to the time period of the time slots of a predetermined cycle period continuously from said recording medium in the closest first time slot assigned to said data reproducing means with the received control command from the time of receiving said control command in the direction reverse to that of said data output from said first bank and storing said data into the second bank; and
a fourth step of outputting said data stored in said second bank at a rate showing the magnification ratio of replay speed specified by said control command.
As described in detail above, with a data reproducing apparatus according to the invention, it is possible for one of its data reproducing means to read data from a continuous region of the data accumulation means for a data reproducing operation in a variable speed replay mode when the volume of image data that can be read out of the data accumulation means is raised. As a result, when said one of the data reproducing means is operating in a variable speed replay mode to realize the specified speed and/or direction of replaying operation, be it high speed replaying, acceleration, deceleration or reversing, it can effectively read out a large volume of image data from the continuous region by a single access so that it can eliminate unnecessary data by thinning out the read out data without giving rise to the effect of slow-speed film and realize the specified speed and/or direction of replaying operation quickly in order to reproduce images.
Additionally, with a data reproducing method according to the invention, again it is possible for one of its data reproducing means of such a data reproducing apparatus to read data from a continuous region of the data accumulation means for a data reproducing operation in a variable speed replay mode when the volume of image data that can be read out of the data accumulation means is raised. As a result, when said one of the data reproducing means is operating in a variable speed replay mode to realize the specified speed and/or direction of replaying operation, be it high speed replaying, acceleration, deceleration or reversing, it can effectively read out a large volume of image data from the continuous region by a single access so that it can eliminate unnecessary data by thinning out the read out data without giving rise to the effect of slow-speed film and realize the specified speed and/or direction of replaying operation quickly in order to reproduce images.